Energy & Power · Study deck

Energy-Aware Case Studies

Picture two field sensors with the same battery where one lasts twice as long.

Battery Bruno is your guide for this deck.

awarecasestudies
Battery Bruno, the module guide, in a scene from this chapter.
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After studying this chapter

Learning objectives

You will be able to:

  • Explain: A case study is useful when it tells you what was measured, what was assumed, and what changed after deployment.
  • Explain: Initial symptom: Firmware entered deep sleep correctly, but whole-board sleep current was far above the estimate.
  • Explain: Transferable pattern: When a field sensor fails a battery target, first inspect the full-period trace.
  • Explain: That point is the next premise in the cell discharges even when the sensor sleeps.
This is the Li-SOCl2 cell the card above names the default for multi-year unattended sensors: 3.6 V nominal with only about 1% self-discharge per year, at the cost of the limited pulse current the same card flags. Photo: みはりん, CC BY-SA 3.0
This is the Li-SOCl2 cell the card above names the default for multi-year unattended sensors: 3.6 V nominal with only about 1% self-discharge per year, at the cost of the limited pulse current the same card flags. Photo: みはりん, CC BY-SA 3.0
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Major section

Start With the Evidence Record

Duty cycle means the share of time a device spends in an active state.

  • This check explains selected workloads and conditions, not every deployment.
  • The deeper cases examine trade-offs, measurement limits, maintenance, and transferable lessons.
  • A case study is useful when it tells you what was measured, what was assumed, and what changed after deployment.
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Major section

Case Study 1: Field Soil Sensor

Shorter connection window and fewer reports.

  • The dominant cost was not the soil measurement.
  • If Baseline cannot be connected to: After revision, the surrounding conclusion is premature.
  • Transferable pattern: When a field sensor fails a battery target, first inspect the full-period trace.
Before-and-after field soil sensor ledger: measurement interval, sleep state, radio behavior, and the review lesson move from a high-current idle loop and full reconnects to deep sleep, a shorter active window, and batched reporting.
Before-and-after field soil sensor ledger: measurement interval, sleep state, radio behavior, and the review lesson move from a high-current idle loop and full reconnects to deep sleep, a shorter active window, and batched reporting.
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Major section

Case Study 4: Board Leakage Failure

Initial symptom: Firmware entered deep sleep correctly, but whole-board sleep current was far above the estimate.

  • The MCU was not the problem; support circuitry stayed powered.
  • Regulator current: The regulator quiescent current was larger than the MCU sleep current.
  • Transferable pattern: A low-power MCU does not make a low-power product.
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Major section

Pattern Map

Current trace shows a real low-current sleep floor and bounded wake window.

  • Upload size, attach time, retries, signal quality, and batching behavior are measured.
  • Accuracy, freshness, missed events, and sensor warm-up are checked.
  • Whole-board sleep current is measured after debug and peripheral shutdown.
Energy case-study pattern map connecting the field soil sensor, asset tracker, vibration monitor, and board leakage cases to reusable review lessons: duty-cycle, communication, sensing, and board repair.
Energy case-study pattern map connecting the field soil sensor, asset tracker, vibration monitor, and board leakage cases to reusable review lessons: duty-cycle, communication, sensing, and board repair.
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Major section

The Cell Discharges Even When The Sensor Sleeps

Its Baseline and ledger labels identify the conditions that must be checked together.

  • That point is the next premise in the cell discharges even when the sensor sleeps.
Use the same evidence chain for battery-chemistry case studies: measure the baseline, identify the dominant drain, change one lever, re-measure under the same boundary, check service impact, and transfer only the lesson.
Use the same evidence chain for battery-chemistry case studies: measure the baseline, identify the dominant drain, change one lever, re-measure under the same boundary, check service impact, and transfer only the lesson.
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Deck summary

Key takeaways

Duty cycle means the share of time a device spends in an active state.

  • Shorter connection window and fewer reports.
  • Initial symptom: Firmware entered deep sleep correctly, but whole-board sleep current was far above the estimate.
  • Current trace shows a real low-current sleep floor and bounded wake window.
  • Its Baseline and ledger labels identify the conditions that must be checked together.
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Retrieval practice

Recall check 1 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q1A case study claims multi-year battery life after changing protocols, but provides no current trace, retry count, or payload size. How should reviewers handle the claimed battery life?

AAccept the claim because the new protocol has shorter airtime.
BReject the claim solely because sensor warm-up could dominate.
CRequest matched before-and-after current, retry, and payload ledgers.
DCopy the claimed lifetime to your product without a current trace.
Show answer

Answer: C A credible energy case study exposes the same evidence boundary before and after the change: payload, timing, retries, sleep current, and service result.

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Retrieval practice

Recall check 2 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q2A vibration monitor saves energy by extracting features locally before upload. Which lesson is safest to transfer to a new design?

AProcess every new workload locally because local computation costs less than the measured radio path.
BCompare local compute charge against the radio energy it avoids.
CStream raw data because the battery and link budget can sustain continuous transfer.
DReuse the same feature algorithm across all sensors and signals.
Show answer

Answer: B A case-study lesson transfers when the underlying evidence pattern matches: data size, compute cost, service requirement, and measurement boundary.

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Retrieval practice

Recall check 3 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q3What changes an energy system in response to measured drain rather than an assumed cause?

ABaseline trace
BDominant drain
CService gate
DTargeted fix
Show answer

Answer: D The change must address the measured drain rather than an assumed one.

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Retrieval practice

Recall check 4 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q4A soil sensor must run unattended for 10 years drawing an average of about 15 uA. Why is a standard Li-ion cell a poor chemistry choice here, even at a generous capacity?

ALi-ion has too little energy density for a small sensor.
BLi-ion self-discharge acts like a large parallel leak.
CLi-ion voltage is too low to power a sensor.
DLi-ion cannot be used below room temperature at all.
Show answer

Answer: B On a 2000 mAh cell, 2%/month is about 40 mAh/month, an equivalent leak near 55 uA - several times the 15 uA load.

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Retrieval practice

Recall check 5 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q5A 2000 mAh Li-ion cell self-discharges at about 2% per month. Modeled as a constant parallel leak, what equivalent current does that represent?

AAbout 3 µA, treating this Li-ion cell like a low-leak primary cell.
BAbout 55 µA, from 40 mAh lost over roughly 720 hours.
CAbout 40 mA, treating the monthly 40 mAh loss as current.
DUse zero current for the estimate because self-discharge is associated with the disconnected state.
Show answer

Answer: B 2% of 2000 mAh is 40 mAh lost per month; dividing by about 730 hours gives 0.055 mA, or 55 uA.

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Retrieval practice

Recall check 6 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q6A design budgets a Li-SOCl2 self-discharge equivalent of 3 uA measured at 20 C, but the sensor is sealed in a dark enclosure that runs near 40 C in summer. What is the most defensible correction to the self-discharge budget?

ALower it because heat slows the cell's chemical self-discharge.
BKeep 3 µA because self-discharge is independent of temperature.
CChange to Li-ion because it is unaffected by summer heat.
DRaise the self-discharge allowance for the hotter sealed enclosure.
Show answer

Answer: D A 20 C to 40 C rise spans two 10 C steps, so the equivalent leak can be on the order of four times the bench figure.

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Print reference

Answers 1 of 2

Answer key.

  1. C · A credible energy case study exposes the same evidence boundary before and after the change: payload, timing, retries, sleep current, and service result.
  2. B · A case-study lesson transfers when the underlying evidence pattern matches: data size, compute cost, service requirement, and measurement boundary.
  3. D · The change must address the measured drain rather than an assumed one.
  4. B · On a 2000 mAh cell, 2%/month is about 40 mAh/month, an equivalent leak near 55 uA - several times the 15 uA load.
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Print reference

Answers 2 of 2

Answer key.

  1. B · 2% of 2000 mAh is 40 mAh lost per month; dividing by about 730 hours gives 0.055 mA, or 55 uA.
  2. D · A 20 C to 40 C rise spans two 10 C steps, so the equivalent leak can be on the order of four times the bench figure.
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